Thermodynamically balanced heat regain system



April 28, 1964 F. M. HENNE 3,130,908

THERMODYNAMICALLY BALANCED HEAT REGAIN SYSTEM Filed Feb. 21, 1962 2 Sheets-Sheet 2 g U P- i m 1% A N 02* N Om A FRED M. HENNE ATT RNEY United States Patent 3,130,998 THERMGDYNAMICALLY BALANCED HEAT REGAIN SYSTEM Fred M. Henne, 104 William Howard Taft Road, Cincinnati 19, Ohio Filed Feb. 21, 1962, Ser. No. 176,858 7 Ciaims. (Cl. 236-49) This application is a continuation-in-part of my co pending application Serial No. 34,195 filed June 6, 1960, now abandoned.

The invention relates to a thermodynamically balanced heat regain system and more particularly to the automatic ventilation of a kitchen in a restaurant or other similar institution wherein cooking operations are relatively continuous over sustained periods of time.

Heretofore, the kitchen or" a restaurant or similar institution was provided with a fan which delivered ventilating air to the kitchen through a usual system of ducting or piping and it was provided for exhausting a fixed quantity of air from the kitchen.

While such prior systems have served to provide ventilation for kitchens, certain difiiculties have arisen with the advent of air-conditioned buildings. Generally speaking, fans of the type employed for ventilating purposes are driven at a substantially constant speed and, hence, deliver a substantially constant volume of air to ducting or piping to which such fans are connected, assuming that the pressure and temperature of the air at the inlet to such fan remain constant. Generally speaking, the effective flow area of the ducting or piping to which such fans are connected is a limiting factor so that the quantity of air delivered by a ventilating fan connected to a system of ducting or piping is fixed or limited by the physical size of the ducting or piping employed. Since the fan is driven at substantially constant speed, the volumetric fiow of air through such a system will remain substantially constant and the rate of flow of air through such a system on a weight basis will either remain constant or will vary depending upon whether the pressure and temperature conditions of the air supplied at the inlet of the fan remain fixed or vary.

Heretofore, it has also been the practice to connect fans of the general type described above to a prime mover such as an electric motor by means of variable drive devices. This allows the use of standard rather than special motors which operate at substantially constant speed and at the same time permit the fan to be selectively driven at a number of different speeds which may be selected by an operator or controlled automatically as the case may be. For any given one operating speed, the characteristics of the fan as well as any ducting to which it may be connected will be as discussed above but through the use of a variable drive means included in the connection between the fan and the driving motor, it is possible to obtain variable volume delivery in such a system by operating the fan at selectively different speeds.

These inherent characteristics of fans and ducting normally employed in connection with ventilating systems, present important problems particularly in the case of airconditioned buildings. Air-conditioning systems for buildings present very difiricult balancing problems not only in reference to heat balance but also air flow and proper distribution thereof. Thus, it is very important that once a proper balance has been obtained in an air conditioning system following its installation, every possible effort should be exerted to avoid upsetting said balance. In the kitchen ventilating systems heretofore employed, variations in the amount of heat transferred to air in the kitchen and resulting from variable cooking loads as well as variations in ambient temperatures necessarily results in certain types of unbalance which prior art ventilating systems have not attempted to control.

Accordingly, it is an object of the present invention to provide an improved arrangement for obviating the above mentioned difliculties.

Still another object of the invention is in the provision of an improved ventilation system for restaurant kitchens in air-conditioned buildings wherein unbalances arising from the operation of the kitchen ventilating system will not adversely afiect the air conditioning system or such adverse effects will be minimized.

A further object of the invention is in the provision of an improved balanced heat regain system for the automatic ventilation of a kitchen in a restaurant or similar institution Where cooking operations are relatively continuous.

Another object of the invention is in the provision of a system for balancing flows of heated air through the utilization of a variable speed fan and a constant speed fan.

A further object of the invention is in the provision of an improved system for the utilization of heated air wherein the heated air and other air are mixed in proper proportions thus eliminating the necessity of a separate heating unit.

Another object of the invention is in the provision of an improved ventilation system employing a variable speed fanthe operation of which is controlled by temperature conditions existing at the inlet side of the fan.

Another object of the invention is in the provision of an improved ventilating system together with means for introducing fresh air into the system in such quantities as may be necessary to provide for a desired air temperature at a selected location within the system.

In general, the invention contemplates thermodynamically balancing quantities and temperatures of air within the system and sometimes subjected to heating eifects therein so that air so heated may be re-used or re-circulated without introducing into said system air from another source which would otherwise have to be initially heated to be operated.

Briefly stated, in accordance with one aspect of the invention a variable speed and a constant speed fan, together with suitable 1 ermost-atic controls, are provided with the speed of the variable speed fan and the position of dampers in a ventilation system related and controlled so as to maintain a pre-selected temperature at a desired location within the system and, at the same time, automatically balance, on a Weight flow basis, the air supplied and the air withdrawn from the system.

Other objects and advantages will be apparent to those skilled in the art from the following description taken in connection with the accompanying drawings in which:

FIG. 1 is a schematic diagram of the apparatus together with the controls.

FIG. 2 is a schematic diagram showing air flow.

In the drawings, the same reference numerals refer to the same parts throughout the several views. It is to be undenstood that the structures and the various means set forth in the specification and illustrated in the drawings are intended not as limiting but as illustrative only in accordance with the statutory requirements since various changes and modifications may be made without departure from the invention.

Referring now to the drawings, the invention is disclosed as embodied in an apparatus which includes fans 11 and 12 which are driven by motors 13 and 14 respectively. Fan 11, which is a variable speed fan is connected at its inlet end to an enclosed chamber 62 such as a kitchen by duct work 15, and at its discharge end to an air mixing box 16 by duct 31). Ducts 15 and 30 constitute an exhaust conduit means. As used herein, the phrase variable speed fan will be recognized by those skilled in the art as denoting a fan connected to its driving motor through a variable speed drive device so that the fan may be driven at a number of different speeds which may be selectively controlled by an oporator or automatically controlled. Such variable speed drive device is a commercially available item, the details of which are not necessary to a proper understanding of the present invention and hence, are not shown.

Mixing box 16 (FIG. 2) functions as a bypass means and comprises a sheet metal box having an opening 17 connected to the discharge end of fan 11. The exhaust duct work 39 is connected to the mixing box at 17 The mixing box also contains a charcoal filter 19. The constant speed fan 12 is connected by means of duct '34 to the mixing box at 20, and is connected to chamber 32 by duct 25. Ducts 25 and 34 comprise supply conduit means for supplying air to chamber 32. The mixing box is connected to duct work for introducing fresh air at 21. As used herein and as will be recognized 'by those skilled in the art, the phrase constant speed fan denotes a fan which is directly or otherwise mechanically connected to its driving motor which operates at substantially constant speed at all times when the motor is caused to be in operation.

In accordance with the invention, there is provided a fresh air damper 22, a return damper 23, and an exhaust damper 24. Air is supplied from the constant speed fan 12 to chamber 32 by duct work such as 25. The .air which is exhausted from the kitchen or working area 32 goes through duct work 15 to the suction or inlet side of the fan 11. The air is discharged from the fan 11 into the mixing box 16. In operation, the speed of fan 11 is controlled by means of a thermostat 26 mounted in duct work 15.

As noted heretofore, fan 11 is a variable speed fan which is capable of operation at a plurality of different speeds so that the volume of air delivered by such fan may vary between substantial limits determined by the characteristics of the variable speed drive device. For example, commercially available variable speed drive devices may allow the volume of air delivered by fan 11 to vary between 4800 and 5800 cubic feet per minute. The speed of fan 11, and hence the volume of air delivered by said fan, is con-trolled by a sensing device or thermostat 25 connected to a potentiometer (not shown) which controls a sheave Wheel (not shown) to regulate the belt drive of said fan.

Constant speed fan 12 is controlled by a dual thermostat 27 mounted Within duct 25. Since fan 12 operates at substantially constant speed, it is capable of delivering only a substantially constant volume of air. Consistent with the example heretofore noted in connection with variable fan 11, the volumetric capacity of fan 12 may be, for example, 4800 cubic feet per minute.

Air discharged from fan 11 into the mixing box 16, depending upon the air temperature sensed by the controlling element of dual thermostat 27 will either move through the mixing box 16 to fan 12, which may or may not be in operation, and through the supply duct work 25, or it may move partly through duct work 25 and partly through exhaust duct 18. When the air passes over thermostat 27, this thermostat functions to cause fan 12 to operate when the temperature of said air is greater than a predetermined minimum temperature which is the temperature setting of the thermostat. The desired temperature setting of the thermostat is accomplished since emostat 27 also controls the setting or position of outside air damper 22, return air damper 23 and exhaust air damper 24, in addition to the operation of fan 12.

Positioning of dampers 22, 23 and 24 is effected by a suitable damper operating means comprising a positioning motor 32 (FIG. 1). It will be understood by those skilled in the art that motor 32. may be electrical or pneumatic or hydraulic or any other suitable type which is capable of producing motion in one direction and also in an opposite direction. Dampers 22, 23 and 24- are connected to motor 32 by a suitable mechanical linkage of any suitable type well known in the art, the details of which are not essential to the proper understanding of the present invention and hence, are not shown.

An aluminum mesh screen (not shown) may extend across fresh air duct opening 21 and the mixed air section of mixing box 16. This screen acts as a condenser due to the conductance of heat through the metal because of the variance in the temperature of the metal screen.

In the operation of such a system, fan 11 is placed in operation firs-t, either manually or through the use of automatic startim means, to withdraw air from the room or kitchen within which is a source of heat such as cooking apparatus. The air so withdrawn is re-circulated and re-introduced into said room or kitchen. Such withdrawal, re-circulation and re-introduction continues until heat from the heat source increases the temperature of the air withdrawn from the room to a temperature greater than the preselected setting of dual thermostat 27.

When this occurs, the density of the air withdrawn through duct 15 has decreased, since density varies inversely with temperature, to a value less than that corresponding to the desired value called for by the setting of dual thermostat 27, this is sensed by thermostat 26 which causes the variable speed drive device to speed up the fan 11; and thermostat 27 automatically starts fan 12 and causes fresh air to be drawn through duct 21 and delivered through duct 25.

In terms of the numerical examples given heretofore, initially and at a predetermined minimum temperature, fan 11 will operate at the lowest speed within the limits of the variable speed drive device. For example, a speed corresponding to a volume rate of 4800 cubic feet per minute. This is also the volume rate of the constant speed fan 12 in the example. When thermostat 26 functions to cause 'fan 11 to speed up and increase its volume rate of delivery, such increase corresponds to the decrease in density of the air withdrawn through duct 15 as compared to the desired density corresponding to the setting of thermostat 27. Hence, ona weight allow basis, the quantity of air withdrawn through duct 15 by variable speed fan 11 always balances the quantity by weight of air delivered by constant speed fan 12 through duct 25.

Dual thermostat 27 is a commercially available item wherein two individual thermostats are encased in a single housing. In accordance with the present invention, the second portion of the dual thermostat is utilized to produce a signal when the limits of a system embodying the present invention have been exceeded so that the system is incapable of delivering air through duct 25 at the temperature setting of the initial portion of thermostat 27. For example, the setting of initial portion of thermostat 27 might require a temperature of 70 and at the same time, heated air withdrawn through duct 15 is at a temperature of 140, and the temperature of the air supplied through duct 21 is In such event, it is impossible to deliver air to duct 25 at 70 irrespective of fan speeds or relative degree of mixing of heated and fresh air. Accordingly, when such a condition exists, the signal produced by the second portion of the dual thermostat 27 may be transmitted to thermostat 26 by connection 36 and functions to modify the signal produced by thermostat 26 and thus shift the operating characteristic of the variable speed drive device to .a diiferent point without otherwise modifying said characteristic. In other Words, the second portion of dual thermostat 27 functions to delay the speeding up of fan 11 when the temperature limits of the system have been exceeded as in the foregoing example without otherwise modifying the function and operation of the various elements of the system.

While a particular embodiment of the invention has been illustrated and described, it will be obvious to those skilled in the art that the various changes and modifications may be made without departing from the invention, and it is intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of the invention.

What is claimed is:

l. A thermostatic balanced heat regain system for supplying a quantity of gas to a chamber from a source and for exhausing an equal quantity by weight of said gas from said chamber to said source, said system comprising exhaust duct means and supply duct means adapted to be connected in parallel between said chamber and source, an exhaust fan in said exhaust duct means and a supply fan in said supply duct means, constant speed power means drivingly connected to said supply fan so as to drive said supply fan at a constant speed, variable speed power means drivingly connected to said exhaust fan for driving said exhaust fan at variable speeds, first thermostatic control means in said exhaust duct means exposed to and heated by the exhaust gases flowing through said exhaust duct means, both said fans having a capacity to move an equal volume of said gas per unit time when the temperature of the gas in said exhaust duct means is at a predetermined minimum temperature, said thermostatic control means operatively connected to said variable speed power means so as to cause the speed of said exhaust fan to increase in proportion to the increase in temperature of the gases in said exhaust duct means above said predetermined minimum temperature whereby said exhaust fan will force a substantially equal weight of said gases through said exhaust duct means per unit time regardless of the temperature of said gases.

2. A thermostatically balanced heat regain system as defined in claim 1 including bypass duct means connected between said exhaust and supply duct means for passing at least some of the gases in said exhaust duct means into said supply duct means, said bypass duct means connected to said exhaust duct means and said supply duct means so as to conduct gas from the outlet of said exhaust fan to the inlet of said supply fan, damper means in said duct means, and located between the exhaust fan outlet and the supply fan inlet, damper operating means operatively connected to said damper means, second thermostatic control means in said supply duct means operatively connected to said damper operating means, said first and second thermostatic control means operable to control said constant speed power means and said damper operating means so that the weight of the gases flowing through said exhaust duct means and supply duct means per unit time will be equal.

3. A thermostatically balanced heat regain system, de-

fined in claim 2 wherein said bypass duct means includes a mixing chamber.

4. A ventilating system including supply conduit means and exhaust conduit means each having an inlet and an outlet, the inlet and outlet of the supply conduit means being adapted to be connected to a supply of gas and to a closed chamber respectively, the inlet and outlet of the exhaust conduit means adapted to be connected to said chamber and supply respectively, an exhaust fan in said exhaust conduit means for exhausting gas from the chamber and a supply fan in the said supply conduit means for supplying gas from the supply to the chamber, variable speed power means drivingly connected to said exhaust fan, constant speed power means drivingly connected to said supply fan, bypass conduit means connected to the exhaust conduit between the exhaust fan and the exhaust conduit means outlet and connected to the supply conduit means between the supply fan and the exhaust conduit means inlet, first thermostatic control means operatively connected to said variable speed power means and located in said exhaust conduit means between said exhaust fan and the inlet to said exhaust conduit means, damper means in the conduit means and located between the out let of the exhaust fan and the inlet of the supply fan, damper operating means operatively connected to said damper means, second thermostatic control means operatively connected to said damper operating means and located in said supply conduit means between said supply fan and the outlet of said supply conduit means, both said thermostatic control means being responsive to the temperature of the gases in said conduit means to operate said variable speed power means and damper operating means so as to cause the flow of gases through said exhaust and supply conduit means per unit time to be equal in weight.

5. A ventilating system as defined in claim 4 wherein said second thermostatic control means is operatively connected to said constant speed power means so as to energize same only when the temperature of the gases flowing through said supply conduit means reaches a predetermined temperature.

6. A ventilating system as defined in claim 5 wherein said second thermostatic control means operates said damper means to cause an increased amount of gases to flow into the inlet of said supply conduit means only after the temperature of the gases flowing through said supply conduit means reaches said predetermined temperature.

7. A ventilating system as defined in claim 4 wherein said damper means comprises a first damper located in said exhaust conduit means adjacent the outlet thereof, a second damper located in said bypass conduit means, and a third damper located in said supply conduit means adjacent the inlet thereof, and said damper operating means being operatively connected to said first, second; and third dampers. I

References Cited in the file of this patent- Engineering Manual of Automatic Control; copyright 1957 by Minneapolic-Honeywell Regulator Company, Minneapolis 8, Minne sota, page 2 A-10 relied upon. Y 

1. A THERMOSTATIC BALANCED HEAT REGAIN SYSTEM FOR SUPPLYING A QUANTITY OF GAS TO CHAMBER FROM A SOURCE AND FOR EXHAUSING AN EQUAL QUANTITY BY WEIGHT OF SAID GAS FROM SAID CHAMBER TO SAID SOURCE, SAID SYSTEM COMPRISING EXHAUST DUCT MEANS AND SUPPLY DUCT MEANS ADAPTED TO BE CONNECTED IN PARALLEL BETWEEN SAID CHAMBER AND SOURCE, AN EXHAUST FAN IN SAID EXHAUST DUCT MEANS AND A SUPPLY FAN IN SAID SUPPLY DUCT MEANS, CONSTANT SPEED POWER MEANS DRIVINGLY CONNECTED TO SAID SUPPLY FAN SO AS TO DRIVE SAID SUPPLY FAN AT A CONSTANT SPEED, VARIABLE SPEED POWER MEANS DRIVINGLY CONNECTED TO SAID EXHAUST FAN FOR DRIVING SAID EXHAUST FAN AT VARIABLE SPEEDS, FIRST THERMOSTATIC CONTROL MEANS IN SAID EXHAUST DUCT MEANS EXPOSED TO AND HEATED BY THE EXHAUST GASES FLOWING THROUGH SAID EXHAUST DUCT MEANS, BOTH SAID FANS HAVING A CAPACITY TO MOVE AN EQUAL VOLUME OF SAID GAS PER UNIT TIME WHEN THE TEMPERATURE OF THE GAS IN SAID EXHAUST DUCT MEANS IS AT A PREDETERMINED MINIMUM TEMPERATURE, SAID THERMOSTATIC CONTROL MEANS OPERATIVELY CONNECTED TO SAID VARIABLE SPEED POWER MEANS SO AS TO CAUSE THE SPEED OF SAID EXHAUST FAN TO INCREASE IN PROPORTION TO THE INCREASE IN TEMPERATURE OF THE GASES IN SAID EXHAUST DUCT MEANS ABOVE SAID PREDETERMINED MINIMUM TEMPERATURE WHEREBY SAID EXHAUST FAN WILL FORCE A SUBSTANTIALLY EQUAL WEIGHT OF SAID GASES THROUGH SAID EXHAUST DUCT MEANS PER UNIT TIME REGARDLESS OF THE TEMPERATURE OF SAID GASES. 